1. Field of the Invention
This invention relates to a recording medium to be used suitably for the ink jet recording method, particularly a recording medium which is excellent in ink receiving characteristic, sharpness of the recorded image, paper feeding and conveying characteristic in a printer, blocking resistance, and also, when said recording medium is transparent, excellent in light-transmittance as well as ink receiving characteristic.
2. Description of the Prior Art
The ink jet recording method performs recording by generating small droplets of ink according to various systems of discharging ink (recording liquid), such as electrostatic attracting systems, systems to give mechanical vibration or displacement to the recording liquid by use of a piezoelectric element or the systems to utilize the pressure of expansion of the recording liquid by heating and ebullition, permitting them to fly and attaching a part or all thereof onto a recording medium such as paper. This method is attracting attention as a method which can reduce noise and realize high speed and multi-color printing.
The inks for ink jet recording are primarily composed of water from the view point of safety and recording characteristics, and most of them contain polyhydric alcohols, etc. added therein for prevention of clogging of nozzles and improvement of discharging characteristic.
As the recording medium to be used for the ink jet recording, there have been employed recording medium comprising conventional paper or comprising a porous ink absorbing layer provided on the base material called paper for ink jet recording. However, with improvement in performance of the ink jet recording device, such as high speed recording or multi-color recording and with popularization thereof, very exacting characteristics are becoming demanded for the recording medium. More specifically, the following requirements are to be satisfied for ink jet recording medium in order to obtain a recorded image of high resolution and high quality:
(1) Fixing of ink to the recording medium is as rapid as possible.
(2) When ink dots are overlapped, the ink attached later should not flow out into the ink dot previously attached.
(3) Although the ink droplets may be somewhat diffused on the recording medium, the size of ink dot should be of the desired size or no greater than the desired size than is necessary.
(4) The shape of ink dot should approximate a true circle, and its circumference should be smooth.
(5) The OD (optical density) of the ink dot should be high, without obscurity around the dot.
Further, in order to obtain a recorded image of high resolution, which is comparable to the color photography, by the multi-color ink jet recording method, in addition to the above requisite performances, the following requirements should also be satisfied:
(6) The color forming characteristic of the coloring components of ink should be excellent.
(7) Since as many droplets as the number of colors of ink may be attached on the same spot overlapped on one another, the ink fixing characteristic should particularly be excellent.
(8) The surface should have lustre.
(9) The medium should have a high degree of whiteness.
(10) The medium should be fed and conveyed smoothly in a printer.
The images by ink-jet recording have been employed only for observation of surface images, but a recording medium is now demanded, which are suitable for uses other than surface image observation, as the ink jet recording device is improved in performance and widely used. The uses other than surface image observation may include those in which recorded images are projected by means of optical instruments such as slides or OHP (overhead projector) on a screen, etc. for observation of those images, color separating plates for preparation of positive plates for color printing, CMF (color mosaic filter) for color display of liquid crystal, etc.
While the diffused light of a recorded image is primarily observed when the recorded image is to be used for surface image observation, the transmitted light passing through the recorded image is a matter of importance in a recording medium to be used in uses other than surface image observation. Accordingly, the recording medium to be used for these uses is required to have excellent light transmitting characteristic, particularly linear transmission factor, in addition to the performances required for recording media for ink jet recording in general as described above.
However, no recording medium has yet been known, which satisfies all of these requisite performances.
Most of the recording media for observation of surface images employ the system in which a porous ink-absorbing layer is provided on the surface and the recording liquid is absorbed into the porous voids to fix the recording agent.
On the other hand, when the surface of the ink absorbing layer is non-porous, non-volatile components such as polyhydric alcohols in the ink will remain on the surface of recording medium for a long time after recording, and a long time is necessary before drying and fixing of the ink, whereby there have been involved the drawbacks such as contamination of clothes or damaging of the recorded images.
European Patent Application No. 0049040 discloses a composite medium for sorbing liquids comprising, in combination, a liquid-sorbent underlayer and, overlying said underlayer, a liquid-permeable surface layer capable of retaining its integrity in contact with said liquid and liquid applying means, the liquid sorptivity of said underlayer being greater than the liquid sorptivity of said surface layer. The composite medium is useful as a recording medium for mechanical plotters employing organic ink. However, the liquid permeable surface layer is primarily intended for retaining the integrity of the surface of the medium to enable the rapid pen movement and to prevent clogging of the tip of the pen caused by gouging of the surface of the medium. On the other hand, the present invention does not require such property of retaining the integrity of the surface since recording means does not contact with the recording medium and the rigidity of the layer overlying the ink-absorbing under layer rather causes troubles: the rigidity of the layer will suppress the swelling of the under layer to reduce the ink-retention ability and to induce blurring.